Method of maintaining an IC-module near a set-point

ABSTRACT

A system for maintaining an IC-chip near a set-point temperature while electrical power dissipation in the IC-chip is varied includes a container having an open end with a seal ring. Located in the container is at least one nozzle for spraying liquid coolant droplets on a portion of an IC-module which holds the IC-chip. This spraying of the liquid coolant occurs while the seal ring is pressed against the IC-module. Also, a pressure reducing means is coupled to the container for producing a sub-atmospheric pressure in the space between the container and the IC-module while the seal ring is pressed against the IC-module.

The present patent application is a Division of a prior patentapplication Ser. No. 10/647,090, that was filed on Aug. 21, 2003, and isentitled “TEMPERATURE CONTROL SYSTEM WHICH SPRAYS LIQUID COOLANTDROPLETS AGAINST AN IC-MODULE AT A SUB-ATMOSPHERIC PRESSURE.

RELATED CASES

The above-identified invention is related to one other invention whichis described herein with a single Detailed Description. The otherrelated invention has U.S. Ser. No. 10/647,091 and is entitled“TEMPERATURE CONTROL SYSTEM WHICH SPRAYS LIQUID COOLANT DROPLETS AGAINSTAN IC-MODULE AND DIRECTS RADIATION AGAINST THE IC-MODULE”. U.S. patentapplications on both inventions were concurrently filed on Aug. 21,2003.

BACKGROUND OF THE INVENTION

The present invention relates to temperature control systems formaintaining the temperature of an integrated circuit chip (IC-chip) neara constant set point temperature while the IC-chip is being tested. Alsothe present invention relates to subassemblies which comprise keyportions of the above temperature control systems.

The IC-chip whose temperature is being regulated typically is part of anintegrated circuit module. In the IC-module, the IC-chip usually ismounted on a substrate and covered with a lid. Alternatively, anuncovered IC-chip can be mounted on the substrate. Any type of circuitrycan be integrated into the IC-chip, such as digital logic circuitry, ormemory circuitry, or analog circuitry. Further, the circuitry in theIC-chip can be comprised of any type of transistors, such as fieldeffect transistors or bipolar transistors.

One reason for trying to keep the temperature of an IC-chip constant,while the IC-chip is tested, is that the speed with which the IC-chipoperates may be temperature dependent. For example, an IC-chip which iscomprised of complementary field effect transistors (CMOS transistors)typically operates faster as the temperature of the IC-chip isdecreased.

A common practice in the IC-chip industry is to mass produce aparticular type of IC-chip, and thereafter speed sort them and sell thefaster operating IC-chips at a higher price. CMOS memory chips and CMOSmicroprocessor chips are processed in this fashion. However, in order toproperly determine the speed of such IC-chips, the temperature of eachIC-chip must be kept nearly constant while the speed test is performed.

Maintaining the IC-chip temperature near a constant set point isrelatively easy if the instantaneous power dissipation of the IC-chip isconstant, or varies in a small range, while the speed test is beingperformed. In that case, it is only necessary to couple the IC-chipthrough a fixed thermal resistance to a thermal mass which is at a fixedtemperature. For example, if the maximum IC-chip power variation is onlyten watts, and the thermal resistance between the IC-chip and thethermal mass is 0.2 degrees centigrade per watt, then the maximumvariation in the IC-chip temperature will only be two degreescentigrade.

But, if the instantaneous power dissipation of the chip varies up anddown in a wide range while the speed test is being performed, thenmaintaining the IC-chip temperature near a constant set point is verydifficult. Each time the power dissipation in the IC-chip makes a bigchange, its temperature and its speed will also make a big change.

The instantaneous power dissipation of a present day microprocessor chiptypically varies from zero to over one-hundred watts. Also, the trend inthe IC-chip industry is to continually increase the total number oftransistors on an IC-chip, and that increases the maximum powerdissipation of the IC-chip. Further, in one type of test that is called“burn-in”, the power dissipation in the IC-chip is larger than normalbecause the voltage to the IC-chip is increased in order to acceleratethe occurrence of failure.

In the prior art, one control system for maintaining the temperature ofa high power IC-chip near a set point while the IC-chip is tested isdisclosed in U.S. Pat. No. 5,821,505 (entitled “TEMPERATURE CONTROLSYSTEM FOR AN ELECTRONIC DEVICE WHICH ACHIEVES A QUICK RESPONSE BYINTERPOSING A HEATER BETWEEN THE DEVICE AND A HEAT SINK”). The '505temperature control system includes a thin flat electric heater whichhas one surface that gets pressed against a corresponding surface on theIC-module, and has an opposite surface which is rigidly connected to acooling jacket that carries a liquid coolant. The corresponding surfaceof the IC-module can be the lid which covers the IC-chip, or the IC-chipitself if there is no lid.

To cool the IC-chip at a maximum rate in the '505 temperature controlsystem, the electric heater is turned off. Then heat quickly travelsfrom the IC-chip through the electric heater to the cooling jacket. Toreduce the rate at which heat travels from the IC-chip through theelectric heater to the cooling jacket, the electric heater is turned onat a low level. To add heat to the IC-chip, the electric heater isturned on at a high level.

However, in the '505 temperature control system, a thermal resistanceexists between the surfaces of the electric heater and the correspondingsurface of the IC-module that get pressed together. This thermalresistance occurs due to microscopic mismatches between the twocontacting surfaces.

The above thermal resistance times the power dissipation in the IC-chipequals a rise in temperature which occurs from the electric heater tothe IC-chip when the electric heater is turned off to cool the IC-chip.This temperature rise limits the maximum power dissipation which canoccur in the IC-chip without causing the IC-chip to overheat and destroyitself. Thus, the maximum power dissipation which can be toleratedwithout destroying the IC-chip is limited by the magnitude of thethermal resistance.

Further in the '505 temperature control system, the electrical heaterinherently has a thermal mass. The larger that thermal mass is, thelonger it takes to change the temperature of the electrical heater.Consequently, the thermal mass of the electrical heater limits the speedat which the temperature of the IC-chip can be regulated.

Accordingly, a primary object of the inventions which are disclosedherein is to provide a totally different structure for a temperaturecontrol systems, which completely avoids the above limitation of the'505 temperature control system.

BRIEF SUMMARY OF THE INVENTION

In accordance with the present invention, a system for maintaining anIC-chip near a set-point temperature while electrical power dissipationin the IC-chip is varied includes an open container having a bottom andsurrounding sides with a seal ring. Located in the bottom of thecontainer is at least one nozzle for spraying liquid coolant droplets ona portion of an IC-module which holds the IC-chip. This spraying of theliquid coolant occurs while the seal ring is pressed against theIC-module. Also, a pressure reducing means is coupled to the containerfor producing a sub-atmospheric pressure in the space between thecontainer and the IC-module while the seal ring is pressed against theIC-module.

When each droplet of coolant hits the IC-module, heat is transferredfrom the IC-module directly to the coolant droplet. The thermalresistance from the IC-module to the coolant droplet is very small. Thusthe thermal resistance limitation, which occurs in the '505 temperatureregulating system, is completely avoided.

The heat transfer from the IC-module to each coolant droplet occurs in atime period Δt which decreases as the difference between the temperatureof the IC-chip (T_(IC)), and the vaporization temperature of the droplet(T_(V)) increases. By maintaining the inside of the container at asub-atmospheric pressure, the vaporization temperature T_(V) is reduced.Thus the difference between T_(IC) and T_(V) is increased, and so thespeed at which each droplet vaporizes and cools the IC-package isincreased from that which would otherwise occur if the pressure in thecontainer is at, or above, atmospheric pressure.

When the total number of droplets that are vaporized per second, timesthe heat of vaporization per droplet, exceeds the power which theIC-chip is dissipating, then the temperature of the IC-chip getsreduced. However, the minimum temperature to which the IC-chip can bereduced is just slightly above the vaporization temperature of thedroplets. Thus, with the present invention, the lowest temperature towhich the IC-chip can be maintained is lower than that which wouldotherwise occur if the pressure in the container is at, or above,atmospheric pressure.

Also, the sub-atmospheric pressure within the container makes the sealring leak tolerant. If a leak occurs between the seal ring and theIC-module, only air will get sucked into the container. No liquidcoolant will leak out of the container onto the IC-module where it couldcause electrical shorts.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an overview of a first embodiment of a temperatureregulating system which incorporates the present invention.

FIG. 2 shows additional details of an array of nozzles which spraysdroplets of liquid coolant, and IR-windows which pass radiation, in theFIG. 1 system.

FIGS. 3A–3D show several patterns of coolant droplets and radiationwhich are sent by the FIG. 2 array.

FIG. 4 shows a set of equations which contain numerical details of onespecific implementation of the FIG. 2 array.

FIG. 5A illustrates one particular benefit which is obtained with theFIG. 1 temperature regulating system.

FIG. 5B illustrates another particular benefit which is obtained withthe FIG. 1 temperature regulating system.

FIG. 6 shows one alternative array of nozzles and IR-windows which canreplace the FIG. 2 array in the FIG. 1 temperature control system.

FIG. 7A shows a second alternative array of nozzles and IR-windows whichcan replace the FIG. 2 array in the FIG. 1 temperature control system.

FIG. 7B shows additional details of the array in FIG. 7A.

FIG. 7C shows further details of the array in FIG. 7A.

FIG. 8A shows a third alternative array of nozzles and IR-windows whichcan replace the FIG. 2 array in the FIG. 1 temperature control system.

FIG. 8B shows additional details of the array in FIG. 5A.

FIG. 9 shows the temperature control system of FIG. 1 incorporating thealternative array of FIGS. 8A–8B and operating on a bare IC-chip whichis mounted on a substrate.

DETAILED DESCRIPTION

One preferred temperature regulating system, which incorporates thepresent invention, will now be described with reference to FIGS. 1, 2,3A–3D, 4 and 5A–5B. An overview of this temperature regulating system isshown in FIG. 1.

In FIG. 1, the temperature regulating system is comprised of everythingthat is shown except item 10. Item 10 is an IC-module (integratedcircuit module) on which the temperature regulating system operates.This IC-module 10 includes components 10 a–10 g, each of which isdescribed in TABLE 1 below.

TABLE 1 Component Description 10a Component 10a is an IC-chip(integrated circuit chip) which is enclosed within the IC-module 10. 10bComponent 10b is a substrate which holds the IC-chip 10a. 10c Component10c is one or more conductors, in the substrate 10b, which carryelectrical power PWR to the IC-chip 10a. 10d Component 10d is one ormore conductors, in the substrate 10b, which carry TEST signals to andfrom the IC-chip 10a. 10e Component 10e is one or more conductors, inthe substrate 10b, which carry TEMP signals from the IC-chip 10a. 10fComponent 10f is a lid which is attached to the substrate 10b and whichencloses the IC-chip 10a. 10g Component 10g is a thermalinterface_material which fills a gap between the IC-chip 10a and the lid10f.

In operation, the FIG. 1 temperature regulating system maintains thetemperature of the IC-chip 10 a near a set-point temperature, while thepower which the IC-chip 10 a dissipates is varied in response to theTEST signals. To accomplish this operation, the FIG. 1 temperatureregulating system includes components 20–34, each of which is describedin TABLE 2 below.

TABLE 2 Component Description 20 Component 20 is a container which hasone open end that faces the IC- package 10. The bottom of the container20 is identified by reference numeral 20a, and the sidewall of thecontainer is identified by reference numeral 20b. Two vacuum ports P arein the sidewall 20b. 21 Component 21 is a seal ring, on the sidewall20b. This seal ring 21 surrounds the open end of the container 20 andforms a seal with the lid 10f of the IC-package. 22 Component 22 is aconduit which has two inputs that are connected to the vacuum ports P inthe container 20, and which has one output. 22a Component 22a is apressure relief valve, in the conduit 22, which can be manually openedto put the inside of the conduit at atmospheric pressure. 22b Component22b is an isolation valve, in the conduit 22, which can be manuallyclosed to block any flow through the conduit. 22c Component 22c is avacuum control valve, in the conduit 22, which opens by a selectableamount in response to a control signal VSET. 23 Component 23 is acondenser/heat- exchanger which has an input port 23a that is coupled tothe output of the conduit 22. 24 Component 24 is a vacuum pump which hasan input 24a that is coupled to the output of the condenser/heatexchanger 23. 25 Component 25 is a control input by which an operatormanually_selects a particular sub-atmospheric pressure for the vacuumpump 24 to generate in the container 20. A signal VSET, from thiscontrol input, indicates the selected pressure and is sent to the vacuumcontrol valve 22c. 25a Component 25a is a vacuum gauge which displaysthe actual sub- atmospheric pressure that is generated in the container20. 26 Component 26 is a reservoir which has an input port 26a that iscoupled to an output port on the vacuum pump 24. 26b Component 26b is anair vent, on the top of the reservoir 26, which enables air to escapefrom the reservoir and which places the liquid coolant in the reservoirat atmospheric pressure. 27 Component 27 is a liquid pump which has aninput port 27a that is coupled to an output port on the reservoir 26. 28Component 28 is a pressure regulator, for a liquid, which has an inputport 28a that is coupled to an output port on the liquid pump 27. 29Component 29 is a conduit which couples an output port 28b on thepressure regulator 28 to an internal channel in the bottom 20a of thecontainer 20. This internal channel is hidden in FIG. 1, but is shown inFIG. 2. 30 Component 30 is replicated multiple times (eg —twenty totwo-thousand times) on the bottom 20a of the container 20. Eachcomponent 30 is a bubble jet nozzle, like those which are in a printerfor a computer. A liquid coolant is sent to each nozzle 30 from theconduit 29 and the internal channel in the bottom 20a of the container20. 31 Component 31 is replicated multiple times, between the nozzles30, on the bottom 20a of the container 20. Each component 31 is a windowwhich passes IR-radiation (infrared radiation) but does not pass anyliquid and vapor that is in the container 20. 32 Component 32 is asource of IR radiation which is coupled to the bottom 20a of thecontainer 20. 33 Component 33 is a control signal generator for thenozzles 30 and the IR source 32. This control signal generator 33receives the TEMP signal on a conductor 33a, and it receives set-pointsignals SP on a conductor 33b. In response to the TEMP and SP signals,the control signal generator produces two control signals CS1 and CS2.The control signals CS1 are sent on conductors 33c to the nozzles 30,and the control signals CS2 are sent on conductors 33d to the IR source32. 34 Component 34 is a manual control input by which an operatorselects a particular set-point temperature. The signal SP from thecontrol input 34 indicates the selected set-point temperature.

Now, the manner in which all of the components in TABLE 2 interact withan IC-package 10 will be described. Initially, one particular IC-package10 which is to be tested is pressed against the seal ring 21, as shownin FIG. 1. Then an operator manually selects a particular set-pointtemperature via the control input 34, and selects a particularsub-atmospheric pressure via the control input 25. Thereafter, the valve22 b is opened. Then, after the selected sub-atmospheric pressure isreached inside of the container 20, electrical power PWR and electricaltest signals TEST are applied to the conductors 10 c and 10 d from anexternal source (not shown). However, if the gauge 25 a indicates thatthe selected sub-atmospheric pressure cannot be reached inside of thecontainer 20 due to a leak past the seal ring 21, then the FIG. 1 systemis shut down and corrective action is taken. This avoids any damage tothe IC-module 10.

Whenever the TEST signals change from one state to another, the amountof electrical power which is dissipated by the IC-chip 10 a alsochanges. Consequently, the temperature of the IC-chip 10 a tends tovary. However, the temperature at the IC-chip 10 a is monitored by thecontrol signal generator 33 via the TEMP signals. And, by properlygenerating the control signals CS1 and CS2, the control signal generator33 is able to keep the temperature of the IC-chip 10 a near theset-point temperature.

To remove heat from the IC-chip 10 a, the control signal generator 33sends the control signals CS1 to a selectable subset of the nozzles 30.Each nozzle that receives the control signal CS1 ejects one droplet ofliquid against the cover 10 f of the IC-package 10. Four ejected liquiddroplets are indicated by the letter “L” in FIG. 1.

When an ejected liquid droplet L hits the cover 10 f of the IC-package10, heat is quickly transferred from the cover 10 f to the liquiddroplet L and that causes the droplet to vaporize. In FIG. 1, vaporizeddroplets are indicated by the letter “V”.

All of the vaporized droplets are removed from the container 20 throughthe vacuum ports P. From those ports, the vaporized droplets travelthrough the conduit 22 to the condenser/heat-exchanger 23.

In the condenser/heat-exchanger 23, heat is removed from the vaporizeddroplets which converts them back to a liquid. Then the liquid from thecondenser/heat-exchanger 23 travels through the vacuum pump 24 tothe_reservoir 26. From the reservoir 26, the liquid travels through theliquid pump 27, the pressure regulator 28, and the conduit 29 to theinternal channel in the bottom 20 a of the container 20.

To add heat to the IC-chip 10 a, the control signal generator 33 sendsthe control signals CS2 to the IR-source 32. In response, the IR-source32 emits infrared radiation as long as it receives the CS2 signal. Thatinfrared radiation passes through the IR-windows 31 and hits the cover10 f of the IC-package 10. In FIG. 1, the infrared radiation isindicated by the dashed lines from the IR-windows 31.

Next, with reference to FIG. 2, additional details will be describedregarding the nozzles 30 and IR-windows 31 which are on the bottom 20 aof the container 20. FIG. 2 shows that the nozzles 30 and IR-windows 31are interleaved in an array of rows and columns. In FIG. 2, there isroom to illustrate only three rows and four columns; however, the actualarray can have any number of rows and columns.

Each nozzle 30 in FIG. 2 receives liquid coolant from an internalchannel which lies within the bottom 20 a of the container 20. Thatinternal channel is coupled to the conduit 29 in FIG. 1.

Each nozzle 30 in FIG. 2 also receives a separate control signal RiCjfrom the control signal generator 33 in FIG. 1. Here, “i” and “j” areindices 1, 2, 3, etc. Control signal RiCj is sent to the nozzle 30 inthe i-th row and j-th column of the FIG. 2 array. All of the controlsignals RiCj together constitute the control signals CS1 in FIG. 1.

Each control signal RiCj is a voltage pulse (or a current pulse) of apredetermined width. When this pulse is received by a nozzle 30, thenozzle ejects a single droplet of the liquid coolant from its orifice 30a. The total amount of liquid coolant which is ejected against the lid10 f of the IC-package 10 is increased by increasing the number ofcontrol signals RiCj which are sent concurrently, and/or by increasingthe repetition rate of the control signals.

All of the nozzles 30 in the FIG. 2 array, as well as all of theconductors that carry the control signals RiCj and all channels thatcarry the liquid coolant, are integrated onto one surface of a planarsubstrate (not shown). The IR-source 32 is attached to the oppositesurface of the planar substrate. That substrate is made of a materialsuch as glass which is essentially transparent to radiation from theIR-source 32. The IR-windows 31 are defined by portions of the substratethat lie between the nozzles 30, through which none of the conductorsfor the control signals RiCj, and none of the internal channels for theliquid coolant, are routed.

Referring now to FIGS. 3A–3D, an example will be described whichillustrates how the signal generator 33 uses the nozzles 30 andIR-windows 31 of FIG. 2 to maintain the temperature of the IC-chip 10 anear the set point while the power dissipation by the IC-chip varies. Ineach of the FIGS. 3A–3D, one complete array of nozzles 30 and IR-windows31 shown. Also, each particular nozzle 30 which is ejecting coolantdroplets is shown by the letter “C” in a circle, whereas each nozzle 30which is not ejecting coolant droplets is shown by the letter C withouta circle. Similarly, each particular IR-window 31 which is passingenergy as infrared radiation is shown by the letter “H” in a circle,whereas each IR-window 31 which is not passing energy is shown by theletter H without a circle.

Assume now that the IC-chip 10 a, in the FIG. 1 temperature regulatingsystem, is dissipating 100 watts of power. In that case, to keep thetemperature of the IC-chip 10 a constant, the amount of liquid coolantwhich is ejected from the nozzles 30 must remove 100 joules of heat persecond from the IC-chip 10 a. This is shown in FIG. 3A as being achievedby ejecting coolant droplets, at a predetermined rate, from the subsetsof nozzles 30 which are shown by “C” in a circle.

Next, assume that the power which the IC-chip 10 a is dissipatingincreases from 100 watts to 200 watts. Then, to keep the temperature ofthe IC-chip 10 a constant, the amount of liquid coolant which is ejectedfrom the nozzles 30 must remove 200 joules of heat per second from theIC-chip 10 a. This is shown in FIG. 3B as being achieved by doubling thenumber of nozzles 30 which are ejecting coolant droplets over that whichis shown in FIG. 3A, and keeping the ejection rate constant.

Next, assume that the power which the IC-chip 10 a is dissipatingdecreases to zero watts. Then, to keep the temperature of the IC-chip 10a constant, the ejection of liquid coolant from each nozzle 30 must bestopped, and all heat which the IC-chip 10 a looses (such as byconduction cooling to the substrate 10 b) must be replaced by infraredradiation through the IR-windows 31. This is shown as being achieved inFIG. 3C. There, the amount of heat which is added to the IC-chip 10 a isincreased (or decreased) by increasing (or decreasing) the ON to OFFratio of the control signal CS2 to the IR-source 32.

The ON/OFF ratio of the control signal CS2 can be varied by generatingthe CS2 signal as a series of pulses at a fixed frequency and varyingthe width of each pulse. Alternatively, the width of each pulse can befixed and the pulse frequency can be varied. Also, the IR-source 32 canhave any internal structure which enables it to emit radiation inresponse to the pulses in the CS2 signal. For example, the IR-source 32can include a quartz lamp which is always on, and further include ashutter which only opens while a CS2 pulse is present.

Next, assume that the power which the IC-chip 10 a is dissipatingincreases to 300 watts. In that case, to keep the temperature of theIC-chip 10 a constant, the amount of liquid coolant which is ejectedfrom the nozzles 30 must remove 300 joules of heat per second from theIC-chip 10 a. This is shown in FIG. 3D as being achieved by ejectingcoolant droplets from a number of nozzles 30 that equals those whicheject coolant in FIG. 3A and FIG. 3B combined, while keeping theejection rate constant.

Now, with reference to FIG. 4, some additional details will be providedregarding the structure of the array of nozzles 30 and IR-windows 31 inFIG. 2. In FIG. 4, equation 1 indicates that the volume of a single dropof liquid coolant which is ejected from one of the nozzles 30 in FIG. 2is ten picoliters, as one practical example. This volume has a weight often nanograms when the liquid coolant is water.

Equation 2 in FIG. 4 calculates the amount of heat ΔQ which can beremoved from the IC-chip 10 a in FIG. 1 by the single drop of water inequation 1. The result of that calculation is ΔQ approximately equalstwenty micro joules per drop. In equation 2, ΔT is the differencebetween the temperature at which the water droplet vaporizes and itsinitial temperature when it is ejected from the nozzle 30, and Cp is thespecific heat of water. Also in equation 2, the term of 2260 joules pergram is the heat of vaporization for water. The heat of vaporization_issignificantly larger than the term (ΔT) (Cp), and so as a roughapproximation, the term (ΔT)(Cp) can be ignored.

Suppose now that the maximum rate at which heat needs to be removed froman IC-chip 10 a is 400 joules per second. Then, equation 3 in FIG. 4expresses that requirement in terms of the heat per drop from equation2, the total number of nozzles 31 in the FIG. 2 array, and the frequencywith which pulses are sent to any one nozzle 30 via the control signalsRiCj.

One particular frequency for the pulses in the control signals RiCj is10 KHz This is stated by equation 4. Then, substituting 10 KHz intoequation 3 and solving for the total number of nozzles 30 in the arrayyields a result of 2000.

Assume now that the lid 10 f on the IC-package 10 has a square area thatis available for heat transfer which is one inch on a side. For such alid, 2000 of the nozzles 30 may be fabricated in a square array whichhas forty-five rows and forty-five nozzles per row. This is stated byequation 5.

When forty-five of the nozzles 30 are equally spaced in each row, thenthe center-to-center spacing of those nozzles 30 is 560 micrometers.This is derived by equation 6.

A single nozzle in a present day inkjet printer occupies an area of lessthen fifty by one-hundred micrometers. This area is stated in equation7. Such nozzles would easily fit in the array of FIG. 2 where therespacing is 560 micrometers.

Also in the array of FIG. 2, there must be room for one of theIR-windows 31 between any two consecutive nozzles 30 in a row. EachIR-window 31 only needs to be larger then the wavelength of infraredradiation in order to pass that radiation, and the wavelength ofinfrared radiation ranges from one to ten micrometers. Thus a largeIR-window 31 of twenty-by-twenty micrometers, as indicated by equation7, will easily fit between the nozzles 30 which are spaced by 560micrometers.

Turning next to FIGS. 5A–5B, three particular benefits which areobtained by the FIG. 1 system, will be described. In FIG. 5A, referencenumeral 40 identifies a single droplet which has been ejected by one ofthe nozzles 30 against a portion of the lid 10 f.

While the droplet 40 is against the lid 10 f, the heat of vaporizationis transferred from the lid 10 f to the droplet 40. That heat transferoccurs while the droplet is_at a temperature T_(V), and it occurs in atime period Δt which decreases as the difference between T_(IC) andT_(V) increases. Here, T_(IC) is the surface temperature of the lid 10 fof the IC-package 10, and T_(V) is the temperature at which the droplet40 changes from a liquid to a vapor.

By maintaining the inside of the container 20 at a sub-atmosphericpressure, the temperature T_(V) is reduced. This increases thedifference T_(IC)−T_(V), and so the heat flux ΔQ/Δt which flows intoeach droplet is increased from that which would otherwise occur if thepressure in the container 20 were at, or above, atmospheric pressure.

In FIG. 5B, reference numeral 40* identifies the droplet 40 from FIG. 5Aafter it has vaporized. When the total number of droplets that arevaporized per second, times the heat of vaporization per droplet, ismore than the power which the IC-chip 10 a is dissipating, then thetemperature of the IC-chip 10 a gets reduced. However, the minimumtemperature to which the IC-chip boa can be reduced is just slightlyabove the temperature where the droplet 40 vaporized. Thus, in the FIG.1 system, the lowest temperature at which the IC-chip 10 c can bemaintained is lower than that which would otherwise occur if thepressure in the container 20 were at, or above, atmospheric pressure.

Preferably, the sub-atmospheric pressure inside of the container 20 iskept at a point where essentially each liquid coolant droplet that isejected from each nozzle rapidly vaporizes as soon as it hits theIC-module. Also preferably, the sub-atmospheric pressure inside of thecontainer 20 is kept at a point where the boiling point of the liquidcoolant is lowered by at least 10° C. from its boiling point atatmospheric pressure.

Further in the FIG. 1 system, the sub-atmospheric pressure which iscreated by the vacuum pump 24 makes the seal ring 21 (as well as thecontainer 20 and the conduit 22) leak tolerant. If a leak occurs betweenthe seal ring 21 and the lid 10 f of the IC-module 10, air will getsucked into the container 20, but that air can get purged from thesystem. By comparison, if the vacuum pump 24 was eliminated and thepressure inside of the container 20 was positive, liquid coolant wouldsquirt out from any leak between the seal ring 21 and the lid 10 f, andthat could cause an electrical short between the conductors 10 c, 10 d,and 10 e on the substrate 10 b.

After one particular IC-module 10 has been tested in the system of FIGS.1–5B, that IC-module is removed and replaced with another IC-module,which is then tested. This sequence is repeated over and over asdesired. To aid in the removal of each IC-module, the isolation valve 22b is closed, and then the pressure relief valve 22 a is opened. Thisenables the inside of the container 20 to be quickly returned back toatmospheric pressure before the IC-module 10 is separated from the sealring 21.

One preferred embodiment of a temperature regulating system whichincorporates the present invention has now been described in detail.Next, with reference to FIG. 6, a second embodiment will be described.This second embodiment is the same as the embodiment of FIGS. 1–5Bexcept that the array of nozzles 30 and IR-windows 31, as shown in FIG.6, replaces the previously described array of FIG. 2.

The difference between the arrays of FIG. 6 and FIG. 2 is that in FIG.6, a single control signal ALLRC is sent to all of the nozzles 30,whereas in FIG. 2, a separate control signal RiCj was sent to eachnozzle. Thus in FIG. 6, the conductors that carry the signal ALLRCoccupy substantially less space than the conductors in FIG. 2 that carrythe signals RiCj.

With the modified array of FIG. 6, all of the nozzles 30 eject onecoolant droplet in response to each pulse in the control signal ALLRC.To increase (or decrease) the amount of heat that is removed per secondfrom the IC-chip 10 a, the frequency of the pulses in the control signalALLRC is increased (or decreased). The particular frequency at any timeinstant is selected by the control signal generator 33 in FIG. 1 whichgenerates the control signal CS1 as signal ALLRC.

When the temperature of the IC-chip 10 a, as indicated by the TEMPsignal, equals the set-point temperature, then the control signalgenerator 33 holds the frequency of the pulses in the ALLRC signalconstant at its current rate. If the temperature of the IC-chip 10 astarts to increase above the set point, then the control signalgenerator 33 increases the frequency of the pulses in the ALLRC signal.Conversely, if the temperature of the IC-chip 10 a starts to decreasebelow the set point, then the control signal generator 33 decreases thefrequency of the pulses in the ALLRC signal. When the frequency of thepulses in the ALLRC signal is decreased to zero, then the control signalgenerator 33 adds heat to the IC-chip 10 a by sending control signal CS2to the IR-source 32, as was previously described in conjunction withFIG. 3C.

Next, with reference to FIGS. 7A–7C, a third embodiment of a temperatureregulating system which incorporates the present invention will bedescribed. This third embodiment is the same as the embodiment of FIGS.1–5B except that the array of nozzles 30 and IR-windows 31′, as shown inFIGS. 7A–7C, replaces the previously described array of FIG. 2.

One difference between the arrays of FIG. 2 and FIGS. 7A–7C is that inFIGS. 7A–7C, the nozzles 30 are clustered together and are surrounded byfour enlarged IR-windows 31′, whereas in FIG. 2, the nozzles 30 andIR-windows 31 are interleaved. Also in the array of FIGS. 7A–7C, thesingle control signal ALLRC is sent to all of the nozzles 30, just likethe ALLRC control signal in FIG. 6.

By separating the IR-windows 31′ from the nozzles 30, as shown in FIGS.7A–7C, all radiation from the IR-source 32 can be directed by opticalcomponents away from the cluster of nozzles 30 and through theIR-windows 31′. Thus in the array of FIGS. 7A–7C, the maximum powerlevel which can be radiated by the IR-source 32, without.cndot.3damagingthe nozzles 30 or their operation, is increased over the array of FIG.2.

FIG. 7C shows one particular structure for the bottom 20 a of thecontainer 20 which includes optical components that direct radiation,emitted by the IR-source 32, around the nozzles 30. Component 51 in FIG.7C is a pyramid-shaped mirror. Radiation from the IR-source 32 isdeflected by the mirror 51 into four beams which are perpendicular toeach other. Two of those beams are shown in FIG. 7C as dashed lines, andthe other two beams (not shown) are perpendicular to the plane of FIG.7C.

Components 52 and 53 in FIG. 7C together form four hollow passageways 54in which the radiation from the mirror 51 travels. Each passageway 54has reflective sidewalls which direct the radiation to the open ends 54a of the passageway.

Component 55 in FIG. 7C is a planar substrate. The array of nozzles 30as shown in FIG. 7B is fabricated on the top surface of the substrate55, and components 52 and 53 are subsequently attached with an adhesiveto the bottom surface of the substrate 55. Four holes 55 a extendthrough the substrate 55 in alignment with the open ends 54 a of thepassageways 54.

All of the holes 55 a in the substrate 55 are covered by a respectivelens 56. Each lens 56 is shaped to spread the radiation that it receivesinto the region over the array of nozzles 30 where the IC-chip 10 a isheld. Alternatively, all of the holes 55 a can be plugged with amaterial which passes the radiation, and a mirror can be located neareach hole to direct the radiation into the region where the IC-chip 10 ais held.

Next, with reference to FIGS. 8A and 8B, a fourth embodiment of atemperature regulating system which incorporates the present inventionwill be described. This fourth embodiment is the same as the embodimentof FIGS. 1–5B except that a single aerosol spray nozzle 61 which issurrounded by four enlarged IR-windows 31′, as shown in FIG. 8A,replaces the array of nozzles 30 and IR-window 31 that are shown in FIG.2.

The aerosol spray nozzle 61 receives liquid coolant from the conduit 29in FIG. 1, and it continuously ejects multiple droplets of the liquidcoolant as long as the control signal CS1 is in an “ON” state. Thosecoolant droplets are ejected in a cone-shaped pattern onto theIC-package 10, which in FIG. 1 is pressed against the seal ring 21.

Preferably, the control signal generator 33 generates the control signalCS1 as a series of pulses which occur at a fixed frequency. To increase(or decrease) the amount of heat that is removed per second from theIC-chip 10 a, the width of the pulses in the control signal CS1 isincreased (or decreased). The particular pulse width at any time instantis selected by the control signal generator 33.

Alternatively, the control signal generator 33 generates the controlsignal CS1 as a series of pulses which have a fixed pulse width. Toincrease (or decrease) the amount of heat that is removed per secondfrom the IC-chip 10 a, the frequency of the pulses in the control signalCS1 is increased (or decreased). The particular frequency at any timeinstant is selected by the control signal generator 33.

To direct the radiation which is emitted by IR-source 33 away from theaerosol spray nozzle 61, the previously described structure of FIG. 7Cmay be used with one modification wherein the array of nozzles 30 isreplaced with the aerosol nozzle 61. Alternatively, the structure whichis shown in FIG. 8B may be used.

In FIG. 8B, the substrate 55 and four lenses 56 from FIG. 7C areretained. Also, a separate IR-source 32 is provided in each of the fourholes 55 a in the substrate 55 that are aligned with the lens 56.Control signal CS2 is sent to all four of the IR-sources 32.

Next, a modification w ill be described which can be made to any one ofthe embodiments of FIGS. 1–5B, FIG. 6, FIGS. 7A–7C, and FIGS. 8A–8B. Forall of those embodiments, FIG. 1 shows that the sidewall 20 b of thecontainer 20 squeezes the seal ring 21 against the lid 10 f of theIC-package 10. However, as a modification, the sidewall 20 b can squeezethe seal ring 21 directly against the IC-chip 10 a.

One example of the above modification is shown in FIG. 9. There, theIC-package 10′ is the same as the IC-package 10 in FIG. 1 except thatthe lid 10 f and thermal interface material 10 g are eliminated. Also inFIG. 9, the bottom 20 a of the container 20 is shown as having thestructure that was previously described in conjunction with FIGS. 8A–8B.Alternatively, the bottom 20 a of the container 20 can have thestructure that was previously described in conjunction with FIG. 2, orFIG. 6, or FIGS. 7A–7B.

Next, a modification will be described which can be made to theembodiment of FIGS. 7A–7C. For that embodiment, FIG. 7B, shows that allof the nozzles 30 eject one droplet of liquid coolant in response to asingle control signal ALLRC. However as a modification, each of thenozzles 30 in FIG. 7B can be sent a separate control signal RiCj, as isshown in FIG. 2.

Next, a modification will be described which can be made to theembodiment of FIGS. 8A–8B. In each of the FIGS. 8A and 8B, only a singleaerosol spray nozzle 61 is shown. However as a modification, two (ormore) aerosol spray nozzles 61 can be held by the substrate 55 betweenthe lenses 56. Also, the same control signal can be sent to all of theaerosol spray nozzles 61 to turn all of them on, or the aerosol spraynozzles 61 can be sent separate control signals.

Next, a modification will be described which can be made to any one ofthe embodiments of FIGS. 1–5B, FIG. 6, or FIGS. 7A–7C. For all of thoseembodiments, each nozzle 30 was described as a bubble-jet nozzle, likethose which are in a printer for a computer. A bubble-jet nozzle ejectsa liquid droplet by heating it with an electric resistor. However as amodification, each nozzle 30 can be a piezoelectric device which ejectsa droplet by squeezing the droplet out of an orifice. Such apiezoelectric device is currently used in Epson printers for digitalcomputers.

Next, a modification will be described which can be made to any one ofthe embodiments of FIGS. 1–5B, FIG. 6, FIGS. 7A–7C, and FIGS. 8A–8B. Forall of those embodiments, FIG. 1 includes an IR-source 32 on the bottom20 a of the container 20. However, when some particular types of theIC-chips 10 a are tested, the electrical power dissipation in theIC-chip never reaches zero. Consequently, to test those types ofIC-chips 10 a, the IR-source 32 and the IR-windows 31–31′ can beeliminated from the embodiments of FIGS. 1–5B, FIG. 6, FIGS. 7A–7C, andFIGS. 8A–8B.

Next, another modification will be described which also can be made toany one of the embodiments of FIGS. 1–5B, FIG. 6, FIGS. 7A–7C, and FIGS.8A–8B. For all of those embodiments, FIG. 1 includes a vacuum pump 23which keeps the inside of the container 20 at a sub-atmosphericpressure. That in turn reduces the minimum temperature at which theIC-chip 10 a can be maintained, and increases the speed at which eachliquid droplet vaporizes, as was previously described in conjunctionwith FIGS. 5A–5B.

However, when some particular types of tests are performed on theIC-chips 10 a, the set-point temperature is so high that asub-atmospheric pressure inside of the container 20 is not needed.Consequently, to perform those tests, the vacuum pump 24 can beeliminated from the embodiments of FIGS. 1–5B, FIG. 6, FIGS. 7A–7C, andFIGS. 8A–8B. Then, the vaporized droplets in the container 20 passthrough the conduit 22 and the condenser/heat-exchanger 23 under apositive pressure which is created by the liquid pump 27 and the vaporitself.

Next, a modification will be described which can be made to thecalculations that are shown by equations 1–7 in FIG. 4. There, thepulses in the control signals RiCj are set by equation 4 and occur witha frequency of ten-thousand pulses per second. However, that is just onespecific example. A practical range for the frequency that can be set byequation 4 is 500 Hz to 500 KHz.

Next, a modification will be described which can be made to theIR-windows 31 and 31′ that are shown in FIGS. 1, 2, 3A–3D, 6, 7A, 7C,8A, 8C, and 9. Those windows pass infrared radiation from the IR-source32 into the container 20 and onto the IC-module 10. But as amodification, the IR-source 32 can be replaced by a substitute source(such as a laser) which radiates electromagnetic energy in a frequencyband other than the infrared band. In that case, the IR-windows 31 and31′ would be modified to pass the energy which the substitute sourceradiates.

Next, a modification will be described which can be made to any one ofthe embodiments of FIGS. 1–5B, FIG. 6, FIGS. 7A–7C, and FIGS. 8A–8B. Forall of those embodiments, FIG. 1 shows that only a single container 20is connected by the conduit 22 to the condenser/heat-exchanger 23.However, as a modification, multiple copies of the container 20 can havetheir vacuum ports P connected by one conduit to thecondenser/heat-exchanger 22. In that case, the output of the pressureregulator 28 would be connected by another conduit to the internalchannel for the liquid coolant in the bottom 20 c of each container 20.

When the above modification is made, each container 20 will hold aseparate IC-module 10 as shown in either FIG. 1 or FIG. 8. Also, thecontrol signal generator 33 will concurrently generate separate controlsignals CS1 and CS2 for each IC-module 10 in response to a separate TEMPsignal from each IC-module.

Next, another modification will be described which also can be made toany one of the embodiments of FIGS. 1–5B, FIG. 6, FIGS. 7A–7C, and FIGS.8A–8B. For all of those embodiments, the description of FIG. 1 indicatedthat the set-point temperature is selected when the testing of anIC-chip begins and remains constant throughout the test. However, as amodification, the set-point temperature can be changed by the controlinput 34 at any time while an IC-chip is tested.

If the set-point temperature is changed while an IC-chip is beingtested, each of the above embodiments of the temperature control systemwill respond very quickly to change the temperature of the IC-chip tothe new set point. This quick response occurs because the amount of heatwhich is removed from the IC-chip by the coolant droplets, and theamount of heat which is added to the IC-chip through the IR-windows, canbe quickly increased or decreased as was previously described inconjunction with FIGS. 3A–3D and FIGS. 5A–5B.

Next, a modification which can be made to the temperature regulatingsystem of FIGS. 8A–8B will be described. In that embodiment, the controlsignal CS1 is sent to the aerosol spray nozzle 61 to thereby increase ordecrease the amount of liquid coolant that is sprayed onto the IC-module10. However, as a modification, the control signal CS1 can be sent tothe pressure regulator 28 in FIG. 1. In that case, the pressureregulator 28 would be structured to increase or decrease the pressure atwhich it sends the liquid coolant to the aerosol spray nozzle, inresponse to the control signal CS1.

Multiple embodiments of the present invention and multiple modificationsthereto have now been described in detail. Accordingly, it is to beunderstood that the present invention is not limited to just the detailsof any one particular embodiment, but is defined by the appended claims.

1. A method of maintaining an IC-module under test near a constantset-point temperature while electrical power dissipation in saidIC-module is varied; said method including the steps of: pressing anopen end of a container against said IC-module such that a leak freeseal is formed between said container and said IC-module while saidIC-module is under test; producing a sub-atmospheric pressure in saidcontainer; spraying a liquid coolant onto said IC-module, from at leastone nozzle in said container, while maintaining a sub-atmosphericpressure in said container; and, keeping said IC-module near saidconstant set-point temperature during testing.
 2. A method according toclaim 1 wherein the temperature of said IC-module is kept, by saidsub-atmospheric pressure, at least 10° C. below the boiling point ofsaid liquid coolant at atmospheric pressure.
 3. A method according toclaim 2 wherein said sub-atmospheric pressure in said container isreduced to a point where essentially all of said liquid coolant fromeach nozzle rapidly vaporizes when it hits said IC-module.
 4. A methodaccording to claim 2 wherein said liquid coolant circulates through acirculation subsystem which is coupled to each nozzle, and wherein saidliquid coolant consists essentially of water.
 5. A method according toclaim 2 wherein multiple nozzles are spaced-apart in said container, andeach nozzle receives one control signal and ejects just a single dropletof said liquid coolant when it receives said one control signal.
 6. Amethod according to claim 5 which further includes the steps of: a)receiving a sensor signal representing a sensed temperature of saidIC-module, and b) sending said control signal to all of said nozzlessimultaneously with a frequency that increases as the differencesbetween said sensed temperature and said set-point increases.
 7. Amethod according to claim 5 which further includes the steps of: a)receiving a sensor signal representing a sensed temperature of saidIC-module, b) sending said control signal to a subset of said nozzlessimultaneously, and c) increasing the number of nozzles in said subsetas the difference between said sensed temperature and said set-pointincrease.
 8. A method according to claim 5 wherein each nozzle ejectseach droplet by squeezing said coolant with a piezoelectric device.
 9. Amethod according to claim 5 wherein each nozzle ejects each droplet byheating said coolant with an electric heater.
 10. A method according toclaim 2 wherein each nozzle receives one control signal and spraysmultiple droplets of said liquid coolant when it receives said onecontrol signal.
 11. A method according to claim 10 which furtherincludes the steps of: a) receiving a sensor signal representing asensed temperature of said IC-module, and b) sending said control signalwith an ON-OFF ratio that increases as the difference between saidsensed temperature and said set-point increases.
 12. A method accordingto claim 2 wherein said seal is formed by encircling a surface on saidIC-module which encloses an IC-chip.
 13. A method according to claim 2wherein said seal is formed by encircling an exposed surface on anIC-chip in said IC-module.
 14. A method according to claim 1, furthercomprising removing said IC-module from said container after testing.15. A method according to claim 14, further comprising pressing the openend of a container against a second IC-module and repeating the steps ofclaim 14 on said second IC-module.
 16. A method according to claim 1,further comprising heating the IC-module with a heater provided withinsaid container when the power of said IC-chip dissipates.
 17. A methodaccording to claim 16, wherein said heater comprises one or moreinfrared heating elements disposed in said container.
 18. A methodaccording to claim 16, wherein said infrared heating elements areinterleaved with a plurality of nozzles.
 19. A method according to claim16, wherein said infrared heating elements surround a cluster ofnozzles.
 20. A method according to claim 1, wherein said set-pointtemperature is colder than the boiling point of said liquid coolant atatmospheric pressure.